I downloaded NSIS. One of the first thinks I checked first is if it was translated to my language. Surprisingly, on the "Contrib\Language files" folder I found a "Valencian" file.
I mean surprinsingly because I would expect to find translations to my language under the "Catalan" name, as Spanish users will find their translation under "Spanish" and not under "Mexican", "Argentinian" or "Iberian", or like the English speakers will rarely find (if ever) their translations under "British", "American" or "Australian" filenames.
The worst think came when I opened the file to check it. It's bad written. Lots of typos, mispelled words, wrong characters. No graphical accents. Nonexistant words. Nothing to do with the Valencian we all learn at the schools. Nothing to do with the language in wich the books I read regularly are written in.
No ISO code exist for a language called "valencian". You will find no references to it in any university or college in the entire world, appart from as a variation of Catalan. The syntax and spelling of valencian/catalan is regulated by a legal entity, depending on the local government, the AcadÃ¨mia Valenciana de la Llengua. You can find it at http://www.avl.gva.es/.
If you don't believe me, you can try and ask them if the language file is correct.
As a Valencian, I ask you to please delete the file. The Catalan translation actually applies as the right Valencian one. But, if you want to keep them as separated languages, at least ask for a correct one. I can send you an updated, corrected and legal valencian translation.
Please take care of my comments. As a Valencian I feel ashamed of having found that file under the name of my mother tongue.